It is common to provide a vehicle with a parking brake such as the drum-in-hat brake disclosed in U.S. Pat. No. 5,180,037 as many of the components derived from conventional drum brakes, such as disclosed in U.S. Pat. Nos. 3,232,391; 6,328,141 and 6,394,237. In such drum brakes the first and second brake shoes are retained on a backing plate through the use of pins that extend through the web of the brake shoes. The pins allow the brake shoes some lateral movement within a brake drum during a brake application when a leading edge of the brake shoe engages the braking surface to allow an abutment surface on a trailing edge of second to be brought in engagement with an anchor to oppose the frictional engagement. On frictional engagement it is necessary that the first and second shoes be able to move however some uneven wear patterns may occur as the webs are not held in alignment with the braking surface on the drum. U.S. Pat. No. 5,246,093 disclosed a brake wherein the web of a unitary brake shoe is retained on the backing plate by a clip member. In this brake, the friction surfaces are ground in a manner such that during a brake application the non-cylindrical surface of the friction material is expanded into a circular shape to function as a parking brake for a vehicle.
It is an object of this invention to provide a simple and effective drum brake wherein the friction surface on a brake pad is retained in a perpendicular alignment with a braking surface during a brake application.
According to this invention, the brake assembly for a vehicle includes a drum that is rotatable about an axis with an inner cylindrical surface defining a braking surface for first and second friction surfaces on first and second brake shoes. The first and second brake shoes are moved by an actuation member from a position of rest to bring the first and second friction surfaces into engagement with the braking surface on the drum to effect a desired brake application. The brake assembly is characterized by a disc that is fixed to the vehicle and has a peripheral surface with a plurality of radial guides interspersed between a first radial abutment and a second radial abutment. A first portion of the plurality of radial guides receive a first arcuate channel member on which the first friction surface is located to align a first reaction surface thereon with the first radial abutment. Similarly, second portion of the plurality of radial guides receive a second arcuate channel member on which the second friction surface is located to align a second reaction surface thereon with the second radial abutment. A spring located between the first and second arcuate channel members urge the first and second reaction surfaces toward the radial abutments while at the same time holding the actuation member and an adjuster arrangement in contact with the first and second arcuate channel members. To effect a brake application assuming forward motion of the vehicle, an input force is applied to the actuation member. The input force initially acts on the first channel to move the first reaction surface away from the first radial abutment and acts on the second channel to move the second reaction surface away from the second radial abutment. When a leading edge on the first friction member contacts the braking surface the first and second shoes rotate with the drum such that the first reaction surface continues to move away from the first radial abutment while the second reaction surface adjacent a trailing edge on the second friction members is brought into engagement with the second radial abutment. When the second reaction surface engages the second radial abutment the force developed by the frictional engagement of the first and second friction members with the braking surface on the drum is opposed and as a result the rotation of the drum is correspondingly reduced in effecting the brake application. The first and second arcuate channels engage the plurality of radial guides such that the first and second friction surfaces thereon are retained in perpendicular alignment with the braking surface during an entire brake application.
An advantage of this invention resides in the manner in which the friction surfaces on a brake shoe are retained in perpendicular alignment with a braking surface on a drum.
Another advantage of this invention resides in the elimination of hold down pins or clips to retain a brake shoe on a backing plate.
A further advantage of the brake shoe of this invention resided in an arcuate channel on which friction material is located such that a first end associated with a first reaction surface is identical with a second end associated with a second reaction end to assist in easy assembly on radial guides on a disc member.
A further advantage of this invention resides in a manner in which a running clearance may be adjusted to set a distance that first and second arcuate channels move to bring first and second friction surfaces into engagement in effecting a brake application.